Warren Ellis has addressed the changes you can expect in Red, the movie based on his and Cully Hamner’s WildStorm/DC Comics title. Here are several excerpts from Ellis’ official website:

So, yes, RED the film is very different. Not least because it needed to generate more material than the book itself actually constituted.

It is in fact best to consider RED as a short story being adapted into film.

Next, and related: RED-the-book is also something of a chamber piece. There are essentially only four characters. (And a lot of people who get killed.) Now, while you can perfectly well make a film with only four characters in â€” or even just one character â€” those films tend not to be massive commercial propositions. And Summit is in the business of making commercial films. Also, they needed to expand RED from a half-hour to an hour-and-a-half. So, yes, there are a lot of new characters.

The tone: no, the film isnâ€™t as grim as the book. The book is pretty grim. But itâ€™s also pretty small. When I sell the rights to a book, they buy the right to adapt it in whatever way they see fit. I can accept that they wanted a lighter film, and, as Iâ€™ve said before, the script is very enjoyable and tight as a drum. They havenâ€™t adapted it badly, by any means. People whoâ€™ve enjoyed the graphic novel will have to accept that itâ€™s an adaptation and that by definition means that itâ€™s going to be a different beast from the book. The film has the same DNA. It retains bits that are very clearly from the book, as well as, of course, the overall plotline. But it is, yes, lighter, and funnier.